Influence of hormones on tumor growth, cell kinetics, estrogen receptor and insulin-like growth factor-I-related protein of human breast cancer (MCF-7) cells transplanted in nude mice.

The influence of estrogens and tamoxifen on estrogen receptor (ER)-positive human breast cancer (MCF-7) cells transplanted into athymic nude mice was investigated. The mice were divided into the following three groups: (1) an E2 group with mice receiving 17 beta-estradiol dipropionate; (2) a TAM group with mice receiving tamoxifen; (3) a control group with mice given no hormone. (1) Tumor growth was significantly increased in the E2 group, but significantly decreased in the TAM group compared to control; (2) the tumor contents of insulin-like growth factor-I (IGF-I) and the rate of IGF-I-positive cells were significantly lower in the E2 group, but significantly higher in the TAM groups compared to control; (3) the IGF-I-positive cell rates were in significant inverse correlation with the [3H]thymidine-labeled cell rates in the E2, TAM and control groups. Thus, the tumor contents of IGF-I and the rate of IGF-I-positive cells were inversely correlated to the tumor growth and the [3H]thymidine-labeled cell rate in this in vivo study, although IGF-I is known to be a mitogen for breast cancer cells in vitro. Further studies are necessary to answer the questions as to the in vivo roles of immunoreactive IGF-I in ER-positive breast cancer.